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#382110 - 08/25/12 08:50 PM Re: Amplifier hum [Re: Ken.C]
grantlyt1 Offline
regular

Registered: 08/25/12
Posts: 8
I live in Australia. I have never seen these cheater plugs.

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#382112 - 08/25/12 08:58 PM Re: Amplifier hum [Re: grantlyt1]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17695
Loc: NoVA
Yeah, I suspect they don't have them there. It's a legacy thing in the States from before we had grounded outlets--a lot of places still don't have them. Basically it disables the ground.
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#382114 - 08/25/12 09:31 PM Re: Amplifier hum [Re: grantlyt1]
Socketman Offline
connoisseur

Registered: 07/12/09
Posts: 1004
Loc: Whitehorse YT
Unless you plan on using the amp in your shower just buck the ground off . Hell my new yamaha reciever came with no ground on the plug. It could also be a polarity problem , house wired incorrectly. Also change out the rca cables, i had a set i used from my kids car that were not that old and they were making my sub hum.
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#382117 - 08/25/12 09:47 PM Re: Amplifier hum [Re: Socketman]
grantlyt1 Offline
regular

Registered: 08/25/12
Posts: 8
I could easily take the ground pin off the 120v side of the plug. It already looks a bit loose. Is it really not that risky to power without the earth pin? I did already try another rca cable but same result. I could purchase a US cheater plug and use it on the 120 volt plug into the step down transformer.

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#382118 - 08/25/12 09:52 PM Re: Amplifier hum [Re: grantlyt1]
Socketman Offline
connoisseur

Registered: 07/12/09
Posts: 1004
Loc: Whitehorse YT
i have no grounds on my kit. i just went through this bs over the past week. You can use it as a test then buy a ground loop isolator if your concerned. You could modify an extension cord also. here are some hum eliminators to look at .

https://www.google.ca/search?q=hum+elimi...120&bih=613


Edited by Socketman (08/25/12 09:54 PM)
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#382119 - 08/25/12 09:53 PM Re: Amplifier hum [Re: grantlyt1]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17695
Loc: NoVA
It is significantly more hazardous with 240V than 120V, but if you're doing it on the 120V side, it shouldn't be THAT big a deal.
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#382120 - 08/25/12 09:55 PM Re: Amplifier hum [Re: Ken.C]
Socketman Offline
connoisseur

Registered: 07/12/09
Posts: 1004
Loc: Whitehorse YT
Originally Posted By: Ken.C
It is significantly more hazardous with 240V than 120V, but if you're doing it on the 120V side, it shouldn't be THAT big a deal.


just wear rubber boots when operating the stereo grin
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#382121 - 08/25/12 10:19 PM Re: Amplifier hum [Re: grantlyt1]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10305
Grantly, welcome. If you mean that there was no hum problem previously with the 875 used for power, and if the connections(with the exception of the Crown connection)were the same, then there appears to be nothing new to create a ground loop. It's possible that there's a defect(e.g., rectifier, filter capacitors)in the power supply section of the Crown.

If it would be a ground loop, using a RCA/XLR adaptor wouldn't be helpful. As Alex pointed out, the balanced circuitry is entirely different, and doesn't simply involve the difference between a RCA plug and XLR connector. The sending unit(875)would have to have a balanced output with two voltages(of opposite polarity)rather than one, which the 875 doesn't have. The wiring itself is just one element and is meaningless without both balanced output circuitry and balanced input circuitry.

Incidentally, although you say that the Crown draws 250 watts "max", that's highly unlikely. Unless a power consumption number is specifically termed "full power" or similar language, the number given is an average one rather than max. Typically, 1/8th of full power is used for the average. For example, 1/8th of 500 is a bit over 60 watts, and at 1/8th power class AB amplifiers are on the order of 20-25% efficient(about 50% at full power). 60 watts output would therefore need about 250 watts of consumption. There's no inconsistency when manufacturers show a consumption number lower than the maximum output number.
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#382123 - 08/25/12 11:03 PM Re: Amplifier hum [Re: JohnK]
grantlyt1 Offline
regular

Registered: 08/25/12
Posts: 8
Problem solved! I just bought a ground loop isolator and the hum is entirely gone. Thanks everyone for your help. grin

Johnk- I am only using a stepdown transformer rated for 500 watts. Does this mean I may blow an fuse on it if I run the amp close to its upper limits?

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#382124 - 08/25/12 11:12 PM Re: Amplifier hum [Re: grantlyt1]
dakkon Offline
connoisseur

Registered: 02/08/04
Posts: 1806
Originally Posted By: Ken.C
I would wager that this has something to do with the step down transformer.


Ken, this is highly likely...Due to the transformer in the the mix this, in of it self could also be the source of the ground loop as this is a new device, and does not address the grounding of that circuit...

How did you wire the ground? If you could post a schematic of how you wired the outlet with the transformer that would help. At this point everyone is hypothesizing as to what you did...


lol... this is what i was just writing as you posted the solution..... oh well!!


With this being said, i would bet the source of your ground loop is the wiring of the outlet off of the transformer.. Again, if you can post a schematic we could help eliminate the ground loop.....


Edited by dakkon (08/25/12 11:16 PM)

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